The goal of the research in this proposal is to identify and to characterize chemical modifications in proteins and peptides by combining classical protein chemistry, traditional analytical methods (e.g., amino acid analysis and protein sequence analysis) and mass spectrometry. This DRR-BRS Shared Instrumentation Grant is for the purchase of a Bio-Ion 20 plasma desorption time-of-flight mass spectrometer, which would be utilized in research projects dealing with: 1) amino-terminal protein processing. 2) immunologic peptides; 3) protein kinases; 4) polypeptide hormones; 5) antibodies in cardiovascular research; 6) autoimmune renal disease, 7) epithelial growth factors, and 8) aminoacidopathies. The completion of these projects depends on the availability of a mass spectrometer capable of determining accurate masses for biologically active proteins and peptides, having a wide range of molecular weights. This will be the only mass spectrometer at the Massachusetts General Hospital, and it will greatly augment the more traditional analytical methods now routinely employed to analyze co-and post-traditional modifications in proteins/peptides and synthetic peptides.